In a post on FB they had the February 1971 American Modeler with Steve Wooley's Cobra. In the article Steve gave some information about how he setup the Fox. Basically, he added one head gasket and OS NVA. He says not to reduce the diameter, (assume this puts it like an ST NVA). He also recommends using 20% nitro fuel, a 10x5 prop (in the photo's it looks like a Rev-up fairly wide blade) and a long reach Fire Ball cold plug. His reasoning was that with the larger diameter spraybar you get better fuel draw and the higher nitro gives you back the power. He does not say what run style he prefers but it is the 70"s do likely 4-2-4. Maybe someone can add to this.

Best,    DennisT

The Cobra setup kinda goes against what was/is considered to be maybe not etched in stone but at least etched in balsa - hot plug, higher compression head, 10% nitro (more seems to break crankshafts with stunt props). Did anyone else fly with Steve and use his Cobra setup on a Fox35/29, how did it do?

Best,   DennisT

 I saw Steve fly quite a few times. I never saw him fly the one that always shows up in pictures. He must have had several over the years. I saw him fly one that had a bubble canopy. None were the light green color. These contest were at Buffalo and i would time my visits to my regional office there so as to go to watch contest. I think a Fox .35 in a Cobra is stretching the Fox to the limit. Some years later i built a cobra and started with a very good ST .35 but soon put in a ST .40. That was a great flying combination and very easy to fly in any conditions.
 A lot of people back then were running the Fox at it’s limit as models were getting larger. Many were using the McCoy .40 red head motor.   
EddyR

Eddy,
Did Steve run the Fox 35 in a 4-2-4 or a rich 2? From the description in article he lowered the compression, put a bigger diameter spraybar, but punched the nitro up to 20%. I guess he wanted the extra fuel draw with the larger spraybar and a softer break (if any) but added nitro to get some additional power back. Maybe to run the 20% nitro with a stunt size prop he needed to back off the compression to avoid pre-ignition (that crackling sound when they get to hot). Seems like there is lots of ways to get the old Fox to run.

  After some probing, because a lot of the people from that era were reticent to tell us what they did, lots of people, or most competitive pilots in the Fox 35 era, were pouring as much nitro in it that the crankshaft could stand. 20. 25. 30% or more. The difference just going from 5% Fox Superfuel to 15% is astonishing as far as power goes. I would also caution it is astonishing how much louder/harsher the exhaust is, too, and since they were typically running open exhaust, that would be a serious consideration now.

    It's a great idea as long as you have a bunch of spare cranks. My observation is that above 15%, the chances of breaking a crank go up dramatically. %5, I would guess that the failure rate is nearly 0, I always ran Superfuel or some equivalent and never broke one. Above 15, from what I have seen, it is just a matter of time. If you were using it for competition thats just the cost of doing business, but that cost was only about $4 a piece.

    Brett

Brett,
I understand running the FOX 35 on the high nitro blends stresses the crank. I think that Steve used the larger spraybar (I assume it is like using an ST NVA) to get stronger fuel drawn, then he used the nitro to compensate but got some pre-igniting or crackling and need to reduced compression (to save the crank). Kinda like flying at Tuson with the thin air.

I have had my Fox's crackle when running a muffler and full 10x6 prop. I solved it by dropping diameter to 9 1/2" to reduce the load (even down to 9" on really hot days) which works well. I like the idea of the stronger fuel draw so might be worth playing with Steve's setup.

Best,     DennisT